Transfer of the Brassica tournefortii cytoplasm to B. napus for the production of cytoplasmic male sterile B. napus

Abstract

The donor‐recipient fusion method was used to combine the cytoplasm of Brassica lournefortii with the nucleus of B. napus for the production of cytoplasmic male sterile (CMS) plants. X‐ray‐irradiated mesophyll protoplasts of B. tournefortii were fused with iodoacetamide (lOA)‐inactivated hypocotye protoplasts of B. napus. Selective conditions of IOA concentrations and X‐ray doses were determined, which resulted in recovery of fusion products and inhibition of further growth of unfused parental cells. In total, 54 plants were obtained from different fusion experiments, of which 25 were verified as cybrids or partial hybrids. Mitochondrial DNA (mtDNA) analyses using 5 mitochondrial gene probes revealed that 20 of the 25 fusion‐derived plants had mtDNA either identical, or with varying degrees of similarity, to B. lournefortii. These plants were classified into four groups on the basis of pollen viability and number. Seven plants were categorised as male sterile since they did not produce pollen or had non‐viable pollen. Of the male sterile plants, five had a mtDNA pattern identical to B. tournefortii and a nuclear DNA content corresponding to B. napus. The nuclear‐mito‐chondrial constitution of these plants thus indicates that the combination of B. tournefortii cytoplasm with the B. napus nucleus results in CMS. Furthermore, mtDNA analysis of the two additional male sterile plants which displayed a rearranged mtDNA, revealed that the only mtDNA similarity shared among all male sterile plants was specific for B. tournefortii atp6 pattern. This indicates that the atp6 region of B. tournefortii may be involved in the expression of CMS.